My first build was in 1985. I built a clone of an IBM XT. Where the IBM machine used an Intel 8088-5 CPU running at 4.77Mhz, I used a NEC V20-10 running at 8Mhz. The CPU was installed in a Taiwanese no-name motherboard. Most computers back then used Monochrome Display Adapter (MDA) video cards that could display text only, no graphics. I opted to go with a Color Graphics Adapter (CGA) video card that could display text and graphics (4 of the ugliest colors imaginable).

When I completed the build and attempted to boot for the first time, no video showed on the display. I took the motherboard back where I bought it. The owner told me that the problem was that I didn't have the motherboard switches set correctly. He installed a MDA card, set the switches to monochrome, attached a monochrome display and it booted right up. I insisted that he show me it working with a CGA adapter installed. He didn't want to do it, claiming it was a waste of time. I insisted, so he finally installed a CGA adapter, set the switches to color, attached a color display and - no video. BTW, computers back then didn't use CMOS to store computer settings as modern computers do, you had to set switches on the MB to indicate things like how much memory was installed, color/mono video, how many floppy drives, etc...

At this time he grabbed the phone and jabbered in Chinese to someone on the other end. After he hung up, he told me to go away and come back in 1 hour. I left for an hour and when I returned, the board was working correctly with a color monitor! Apparently in that 1 hour, whomever he called on the phone, made corrections to the ERSO (Taiwanese) BIOS and the new BIOS was burned and installed on the board. Apparently, I was the first to ever attempt a build with a CGA video adapter with that MB/BIOS combo. At any rate, I was now happy as my first build was fully functional and overall it was a positive experience.

I was given a 386SX by somebody. It was pretty much a pile of junk, and so the next computer show (there were computer shows every three months or so back then), I went and bought a new motherboard, AMD 486 processor and a decent video card.

Several months later, I threw in a sound card and bought a new monitor. I was single and actually had money then.

A few months after that, I built a computer from scratch for my girlfriend.

A few months after that, I bought a top-of-the-line system off a guy for next to nothing. It was a custom-build, bleeding-edge high speed Pentium in full tower, and the guy built it himself. Problem was, it kept crashing on him at random, and he hadn't the energy (or requisite knowledge, apparently), to troubleshoot it and fix it, so I got a $2,000 system for $350.

The problem, it turned out, was that he had the wrong parameters punched into the BIOS for his hard drive. Sad thing was, that particular motherboard had an autodetect feature that worked perfectly fine for the drive. Even worse, he gave me all the literature for the parts he bought and the parameters for the drive were right there in the manual for it.

In all my builds, I mostly ran into problems with plugging the drive cables in wrong, (or them pulling out) and one time I had managed to get a boot-sector virus on a Windows boot disk that took me a couple days to figure out.

My first build went rather well. It wasn't all that far ago. Around the time I joined this forum.

The only issue I had, was that I didn't plug in the ATX 12v connector into the motherboard, so it wouldn't boot.
I wondered why for around an hour, before it hitting me that there was a power connector socket left to be connected haha.

My first PC was a 386. My dads work was throwing away broken PCs so I thought I would take them home, take them apart and make working machines. Was such a great experience for me. I was so excited when I found out my PC had a TURBO button LOL

It served me well. The only problem I had on build was that the case came with a faulty power button, so I was pretty heartbroken when the system wouldn't turn on, but after I learned how to cross the power pins, and it fired right up, I took the case in and had them fix the switch.

Heh, my first build was a $350 gaming computer, that I used some old compaq case for :P
I had to put in different holes to mount the PSU, and generally rig everything haha. I even put my own window in it, damn that thing was awesome =P

The best part? I sold it 2 years after I built it, and made a /profit/. Was awesome hahahaa.